1. Field of the Invention
This invention relates to a method and apparatus for cooling bus bars in an electrical circuit which requires control of its operating temperature for effective functioning.
2. Background Art
Power can be distributed in many ways in electronic systems. Power distribution in a high current environment (e.g., 25-2,500 amps) requires moving the current from a power supply to various components, such as amplifiers, rectifiers, routers, servers, etc. Among the more common methods used are those that involve heavy gauge wire and cable, circuit boards, and copper bus bars.
Historically, solutions to power distribution have involved one or more heavy copper bus bars that are provided with holes for connecting cables. Typically, the bars might be spaced apart from each other and be isolated by insulating spacers. Large copper or aluminum bus bars and cables have been used for years to distribute power within industrial control and telecommunication cabinets. They are large and can carry high power relatively easily. Traditionally, if the bus bars became hot from excessive current, more air was moved within a cabinet to cool them. If the bars were uninsulated (and thus perilous to the touch), they tended to be located remotely for safety reasons. In such a setting, cables were run to connect the bars to the components.
Today, however, the quest continues for higher power in smaller packages. It would be desirable to engineer power distribution systems that can operate at higher temperatures so that more power can be distributed within a system. Additionally, the packaging engineer contends with the problems of air flow and ventilation, vibration, noise, and efficient use of space.
In light of problems that are unsolved by previous approaches, it would be desirable to provide a cooling system for electrical components or conductors such as bus bars that increase the current-carrying capacity of the bus bar, while reducing its size, thereby saving space and weight.
Illustrative of prior art approaches is an evaporative spray coolant for cooling a heat source as described in U.S. Pat. No. 5,220,804, which issued on Jun. 22, 1993; and a method for cooling a heat source as described in U.S. Pat. No. 6,060,966, which issued on May 9, 2000.
The invention is a method for cooling bus bars in order to increase their current-carrying capacity while saving space and weight. The method comprises the steps of:
providing a housing having an interior wall;
locating a distribution manifold within the housing, the distribution manifold comprising a pair of hollow bus bars;
communicating to the manifold a supply of an evaporative coolant;
delivering the coolant under pressure through the bus bars so that upon exiting the manifold, the coolant impacts the external surface of the bus bar and/or other adjacent surfaces, so that a portion of the coolant undergoes a phase change from the liquid to the vapor state. Heat is extracted from the components at least as quickly as heat is generated by the flow of current. The extraction of heat maintains or lowers the temperature of the bus bar and enables a given size of bus bar to carry more current within an acceptable rise in temperature.
The invention also includes an apparatus for cooling bus bars in an electrical circuit. The apparatus comprises a circuit board and a plurality of bus bars mounted to the circuit board. Between at least some of the bus bars is an enclosed space which defines a distribution manifold through which an evaporative coolant flows.
The bus bars are mounted in close proximity with each other, thereby saving space and weight in the electrical circuit and providing good electrical noise immunity.